The effect of the structure changes of 4 series of bisammonium salts of N,N′-bis(alkyldimethyl)-3- X-1.5-pentanediammonium dibromides type, where the alkyl chain (R) had 6 to 18 carbon atoms and X = CH 2, NCH 3, O, or S upon the surface active and aggregation characteristics of their aqueous solutions was examined. The critical micelle concentration (CMC) was investigated by the tensiometric and conductometric methods. The concentration of surface saturation (Γ max) and surface area per molecule ( F) were calculated from the slope - ( d γ d log c ) T of the decreasing parts of surface tension lines vs log c. The change of standard Gibbs' energy of micellization (− ΔG m) was established from CMC data. From log CMC = A - B(n CH 2 ) relationships the equivalent chain lengths ( n CH 2 ) eq and hydrophobicity indexes ( I) were calculated for each series of compounds. It was found that the CMC does not reflect the fine changes in sufficient measure in comparison of molecules with the similar structure, while I represents a convenient parameter which can include the electronic and spatial changes appearing as a consequence of structural change. The anomalous courses of some relationships were elucidated in terms of spatial arrangements and weak intermolecular interactions. The isosteric exchange of the CH 2 group in position 3 of the joining bridge by sulfur results in the most lipophilic molecules, followed by the reference series of 1,5-pentanediammonium derivatives; the series with NCH 3 group differs from it only slightly. Most hydrophilic are the 3-oxa derivatives. Such lipophility sequence was determined from I, but also from F and surface tension at CMC ( γ CMC) values and from regression equations.